Currently, Wikipedia states some examples of borrowed chords in major keys that are shown below: The thing is, the vii°7, IV♭7, and the V♭9 look too worrisome to me. Although I definitely agree with ii°, iiø7, ♭III, iv, ♭VI, and iv♭7. Another issue is that the borrowed tonic chord is not shown.
Based on my theory and how I have learned from my instructor, one key will have at least seven borrowed chords built on all seven scale degrees. In major keys, the borrowed chords will be derived from the natural minor scale, which means they must be diatonic to the parallel natural minor. In the key of C-major, the minimum number of seven chords will appear as below:
- Cm (C: i)
- Ddim (C: ii°)
- E♭ (C: ♭III)
- Fm (C: iv)
- Gm (C: v)
- A♭ (C: ♭VI)
- B♭ (C: ♭VII)
Other types of chords can be borrowed (seventh for example), as long as they are diatonic to the parallel natural minor.
Wikipedia also currently states over a borrowed chord in minor keys that are derived from the parallel major:
The question here is, is there only one borrowed chord in minor keys? I know that the Picardy third is the borrowed tonic that appears at the final cadence of a piece.
I've been instructed that there are at least seven, which is the same for major keys. Since there is only one major scale, we get the following in the key of a-minor, as borrowed chords have to be diatonic to the parallel key:
- A (a: I)
- Bm (a: ii) (Also diatonic to the melodic minor)
- C♯m (a: ♯iii)
- D (a: IV) (Also diatonic to the melodic minor)
- E (a: V) (Also diatonic to the harmonic and melodic minors)
- F♯m (a: ♯vi)
- G♯dim (a: vii°) (Also diatonic to the harmonic and melodic minors)
Now, the question is, is the Wiki more accurate, or am I? Wikipedia sometimes tells false things as people can edit. If I am actually true, then I will edit the Wiki to my definition.